1. Field of the Invention
The present invention relates to a pattern inspection apparatus for inspecting pattern defects of a plate to be inspected where micropatterns are formed, e.g., a photomask used in a manufacturing process of a semiconductor integrated circuit.
2. Description of the Related Art
A pattern size of a large-scale-integrated circuit (LSI) has been reduced more and more in recent years, and it is expected that products having minimum line widths of 0.1 μm or lower will be mass-produced in the near future. Such downsizing has been accompanied by an extremely small defect dimension to be detected, which makes it essential to develop a pattern inspection apparatus for inspecting patterns of an LSI, and pattern defects of a transfer mask used for LSI manufacturing.
Conventional pattern inspection methods are mainly classified into die-to-die comparison, in which two chips of similarly written patterns are observed by different detectors, and a difference between the two is detected by comparison based on a defect detection algorithm, and die-to-database comparison, in which a chip of a written pattern is observed by a detector, which is then compared with designed pattern data by a defect detection algorithm to detect a defect.
In the die-to-die comparison method, since the two chips of the similarly written patterns are observed, there is a drawback of impossible detection of the defects if similar defects are present. On the other hand, in the case of the die-to-database method, even if no such problem occurs because of the comparison with the designed pattern data, there is a drawback of noncoincidence between detected image data and reference pattern image data, which causes false defects. Consequently, highly sensitive and highly accurate inspection is difficult.
Thus, the die-to-die comparison method and the die-to-database comparison method have advantages and disadvantages, and there is a demand for an inspection apparatus which can combine these methods well. However, in the case of combining the two methods, the following problems occur, especially when the die-to-die comparison method is used.
That is, since there is variance in dimensions of dicing portions between chips on a mask to be inspected and there is no repeated pattern in a peripheral pattern portion, it is impossible to carry out a simple step of obtaining a dimension of one chip at equal distribution. Thus, it is necessary to teach a repetition start position of the chip to the apparatus by an operator's operation based on an instruction manual. At present, by using feature pattern shapes, the operator visually verifies a start position, a finish position etc., of each chip. Consequently, operation mistakes by the operator and setting variance easily occur, which leads to a problem of reduction in inspection accuracy.
Therefore, there is a demand for a pattern inspection apparatus which can prevent operation mistakes by the operator and setting variance in the die-to-die comparison method, and improve operability and inspection accuracy.